The smooth softshell turtle (''Apalone mutica'') is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of softshell turtle of the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Trionychidae The Trionychidae are a taxonomic family of a number of turtle genera, commonly known as softshell turtles. The family was erected by Leopold Fitzinger in 1826. Softshells include some of the world's largest freshwater turtles, though many can a ...

. The species is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...

to North America.

Geographic range

''A. mutica'' is native to North America. It is distributed throughout the central and southcentral United States as its geographic range extends from western Pennsylvania to New Mexico and south to the Florida panhandle. Smooth softshells turtles inhabit the

Mississippi River The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it fl ...

drainage from Louisiana up to North Dakota and Pennsylvania, as well as the Colorado, Brazos, Sabine, and Pearl, Alabama and Escambia river systems. Two subspecies of ''A. mutica'' have been identified. The midland smooth softshell, ''Apalone mutica mutica'', is found throughout the central United States. The other subspecies, ''Apalone mutica calvata'', is found ranging from Louisiana to the panhandle of Florida.

Habitat

Both subspecies of ''A. mutica'' are typically found in medium to large unpolluted rivers with moderate to fast currents, but are also found in standing water bodies like lakes, ponds and marshes. They prefer water with sand or mud bottoms, without rocky areas or dense vegetation. Sandbanks must also be present.

Description

The smooth softshell turtle has an anapsid skull. This kind of skull is present among the earliest reptiles and is retained by turtles today. The anapsid skull lacks openings behind the orbits. The smooth softshell turtle has a smooth, flexible and leather like carapace that is covered by skin instead of the hard scutes commonly observed in other turtle species. The plastron is light (white or gray) with no markings, and the underlying bones are visible. Smooth softshell turtles have a tubular snout with round nostrils. Ernst C, Lovich J (2009). ''Turtles of the United States and Canada, Second Edition''. Baltimore, Maryland: The Johns Hopkins University Press. 840 pp. .

Sexual dimorphism

There is sexual dimorphism between females and males of ''A. mutica'' as females are larger than males. A female has a carapace length of compared to a carapace length of for males. Additionally, the female smooth softshell turtle is usually brown or olive-colored with irregular dark brown blotches, while the carapace of males and juveniles is a brown or grayish color with dark dots or dashes. Sexual dimorphism is also apparent in the size of the tails and claws. Males have thicker tails than females, but females have longer hind claws than males.

Similar species

The smooth softshell turtle may be easily confused with the spiny softshell turtle (''Apalone spinifera''), as the differences between the two species are subtle. The spiny softshell turtle has a rough carapace with spines along the front edge while, as the name implies, the smooth softshell turtle lacks such spines.Oldfield, Barney; Moriarty, John J. (1994). ''Amphibians and Reptiles Native to Minnesota''. Minneapolis, Minnesota: University of Minnesota Press. 237 pp. . Additionally, the white chin and throat of the smooth softshell are unmarked, compared to the splotchy chin and throat of the spiny softshell. ''A. mutica'' is the only species of North American softshell with round nostrils; all other species have ridges on the nasal septum which make the nostrils C-shaped.

Diet

The smooth softshell turtle is mostly carnivorous, eating aquatic insects, crayfish, fish and amphibians. Although primarily carnivorous, it sometimes resorts to eating vegetation such as algae, vegetables, fruits, and nuts.

Reproduction

Breeding of the smooth softshell turtle occurs from April to June. The mating system utilized by these turtles is polygyny, meaning that males will mate with more than one female. Males actively seek out females by approaching other adults. If the other party is male or a non-receptive female, aggression may be displayed. However, if the other party is a receptive female, she remains passive to the advancements of the males. Copulation usually occurs in deep pools as the male mounts the female. The nesting period is usually from May to July as females only lay eggs once a year. During this period, adult females of ''A. mutica'' lay clutches of 3 to 28

eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...

not more than from water in sandy areas. Eggs generally hatch 8 to 12 weeks later with the highest frequency of hatching being between August and September. Hatchlings average a weight of and have a carapace length of . Male smooth softshell turtles become sexually mature during their fourth year and females become sexually mature during their ninth year. Female turtles offer prenatal care for their offspring. They produce high levels of non-polar lipids that provide energy for their growing embryos.Nagle, Roy D., et al. (2003). "Parental investment, embryo growth, and hatchling lipid reserves in softshell turtles (''Apalone mutica'') from Arkansas." ''Herpetologica'' 59 (2): 145-154. This energy is more than enough to keep the embryos alive. The high concentration of lipids also offer an advantage at birth as it acts as a food source until they hatchlings become mature enough to commence feeding. This type of care is also known as parental investment in embryogenesis. However, after hatching no physical parental care is given.

Life history

The smooth softshell turtle is the most aquatic of the softshell turtles as it is often referred to as a "swimmer". It is able to stay underwater for extended periods of time due to its long neck and tubular snout. It often buries itself in the sand substrate at the bottom of a river or pool just deep enough so that its snout barely reaches the surface. Additionally, the skin covering the shell allows for a high rate of gas exchange. This enables the turtle to stay submerged for a long period of time. In this position, it often waits for prey to pass and utilizes its long neck to capture the prey. The smooth softshell turtle hibernates in the months of October to March. It hibernates by burying itself in substrate underwater. After emerging from hibernation, it is often found on land basking in the sun. Given that its shell is a soft shell, it is unable to stay in the sun for extended periods of time. When basking, it is wary of its surroundings, and if any threat presents itself, it is quick to abandon its basking site to seek safety. Its agility on land and water makes it a difficult prey item for predators such as raccoons, humans, alligators and snapping turtles. It seeks shelter from these threats by diving and concealing itself in mud.

Conservation status

Currently, the smooth softshell turtle is considered a species of least conservation concern. However, the species is still facing some wide-ranged threats. These threats include habitat degradation, harvesting for food, and an increase in human disturbances at nesting sites. Additionally, due to its skin's high rate of gas exchange, it is very susceptible to polluted waters. As a result of all of these factors, the smooth softshell turtle has been listed as a species of special concern in Minnesota and Wisconsin.

Subspecies

Two subspecies are recognized, including the

nominotypical subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...

. *'' Apalone mutica calvata'' *'' Apalone mutica mutica'' ''

Nota bene (, or ; plural form ) is a Latin phrase meaning "note well". It is often abbreviated as NB, n.b., or with the ligature and first appeared in English writing . In Modern English, it is used, particularly in legal papers, to draw the atten ...

'': A trinomial authority in parentheses indicates that the subspecies was originally described in a genus other than ''Apalone''.

Sympatric species

''Apalone mutica'' is sympatric with the spiny softshell turtle ('' Apalone spinifera'') over much of its range.Williams, Thomas A.; Christiansen, James L. (1981). "The Niches of Two Sympatric Turtles, ''Trionyx muticus'' and ''Trionyx spiniferus'', in Iowa". ''Journal of Herpetology'' 15 (3): 303-308
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